The quest for minimum backlash or backlash take-up in gearing teeth is a constant preoccupation in horology. The difficulty lies in the inevitable variations in distance between centres, due in particular to operating backlash in the pivots. Flexible toothings may be used to compensate for these variations in distance between centres; however their design is complex, due to their energy consumption and thus their impact on the overall efficiency of the gear train. An example is given by EP Patent No 2003522 in the name of Chopard Manufacture SA, which discloses a toothed, backlash take-up wheel with alternate rigid teeth and flexible teeth. This wheel cooperates with a drive wheel having rigid teeth, the rigid drive tooth is clamped between the rigid tooth and the elastic tooth of the driven wheel, so as to take-up the gear backlash via permanent contact between the rigid tooth of the driving wheel and the meshing flank of the driven wheel.
This geometry is preferably devised for one direction of rotation, and is ill-suited to a change of gearing direction. Moreover, with use, known flexible wheels are known to be very sensitive to wear.
WO Patent Application No. 2012/037593 A2 in the name of Miba Sineter Austria GmbH discloses another wheel with a differential arrangement of teeth in the direction of the thickness of the wheel plate. This wheel includes several materials of different elasticity.
The problem is therefore to take up play and prevent any display problems when there is a change of direction, for example during time-setting.